there are a couple of possible meanings of "i don't get this"; that could mean you don't understand the wording of the problem in the first place, or, alternatively, it could mean that you understand the problem's wording just fine but don't understand its solution.

so, let's just look at everything.

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WORDING

"amounts proportional to the number of scenes in which..."
means:
the dollar amounts are in the SAME RATIO as the numbers of scenes, viz., A:B:C:D = 21:7:4:3.

--

OPENER

the most important thing you should take away from this problem:
whenever you have a RATIO with NO pre-existing information about the quantities - i.e., no actual numbers and no algebraic expressions - define algebraic expressions by multiplying each of the coefficients in the ratio by the variable x.
(this technique is called "the unknown multiplier" in our manhattan gmat courses.)

so:
dollar amount A = 21x
dollar amount B = 7x
dollar amount C = 4x
dollar amount D = 3x

once you have this, it's fairly clear that the question can be REPHRASED as: what is x?

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STATEMENT (1)

21x + 7x = 560,000
you can find x
sufficient
(note that there's no need to actually find x)

--

STATEMENT (2)

7x = 4x + 60,000
you can find x
sufficient
(again, no need to actually find x)

--

ans = d